The present invention relates to a cooling device and electric equipment including the cooling device, such as blade servers.
In recent years, in blade servers, for which demand has been rapidly growing, further increase in information processing capability and space saving have been required. The information processing capability has been drastically enhanced year after year with enhancement in the performance of a single CPU. Further, by increasing the number of CPUs loaded on one blade, enhancement in the information processing capability per one blade is designed. Further, by reducing the thickness of a blade, the number of blades which can be loaded on one rack is increased.
By increase in heat generation amount following enhancement in performance of a CPU, and reduction in thickness of a blade, the heat generation density of the blade server is drastically increased. Therefore, enhancement in cooling efficiency is desired. Further, the blade servers realize high reliability by redundant design and maintenance during operation. In order to realize maintenance during operation, blades and the respective units such as a power supply unit, and fan unit are required to be attached to and detached from the rack during operation of the blade server. This is called hot swap, and is the characteristic of the blade server. Therefore, the cooling device which is loaded on the blade needs to be attachable and detachable.
Here, describing the typical configuration of a blade server, the blade server is loaded with several chassis in the rack. The chassis is loaded with a plurality of blades, power units, fan units, system units and I/O units. The blade, fan unit and I/O unit are respectively connected to the system unit through back planes. The blade which is an information processing device is loaded with electronic components such as a CPU, a memory, a chip set, and a hard disk (HDD).
The cooling method which is a mainstream at present is a method for cooling each of the electronic components by causing air to flow into the blade by a fan module loaded on a chassis. A CPU which has a large heat generation amount among the electronic components is mounted with a heat sink made of a material with a high thermal conductivity such as copper and aluminum. The heat sink mounted to the CPU has been increasing in size year by year with increase in the heat generation amount of the CPU, and enhancement in performance such as incorporation of a heat pipe has been designed.
However, while the heat generation amount of a CPU is increasing and blade thickness is being reduced, air-cooling of the CPU in the blade by attaching the heat sink to the CUP is approaching its limit.
Thus, a cooling system is conceivable, which transports generated heat of a CPU to the outside of the blade to radiate the heat by using a liquid circulating type heat transport device and a phase change type heat transport device. According to the cooling system, a large radiator and chiller can be applied as heat radiation means outside the blade, and therefore, the cooling system can handle with a large heat generation amount of the CPU. Meanwhile, in this cooling system, realization of hot swap becomes a problem. As solution means for it, there is a method for connecting the heat transport device in the blade and the heat transport device outside the blade by using a coupler. However, connection with a coupler has the risk of leakage of a liquid.
Thus, in order to prevent leakage of a liquid, use of a cooling system in which the heat transports devices inside the blade and outside the blade are completely closed is conceivable. In this cooling system, it is a heat pipe that is considered to be the most effective as the heat transport device in the blade.
A heat pipe is a device in which in a completely tightly closed pipe from which non-condensed gas is excluded, a working fluid evaporates at the heat receiving side where the heat pipe and the heat generating source are in contact with each other, and the vapor flows in the pipe and condenses at the heat radiation side in contact with a heat exchanger, whereby heat is transported. The working fluid condensed at the heat radiation side is transported to the heat receiving side by gravity and capillary force, and continuous operation Is enabled.
Conventionally, in the heat pipe, reduction in the thermal resistance and enhancement in the maximum heat transport amount have been designed. Here, the heat transport amount means the heat amount flowing to the heat radiation side from the heat receiving side of the heat pipe. The thermal resistance means the temperature difference between the heat receiving side and the heat radiation side of the heat pipe per unit heat transport amount. To have small thermal resistance means to be capable of transporting the same heat amount with a small temperature difference. When the heat transport amount reaches a certain fixed heat transport amount in a heat pipe, transport of the working fluid which is condensed at the heat radiation side to the heat receiving side is inhibited by, for example, the force of the vapor which generates at the heat receiving side, and the boiling surface at the heat receiving side runs dry (dries out) whereby the heat pipe cannot exhibit the performance. The cause of the heat transport limit is not limited to only such interference of the vapor and the working fluid. The largest heat transport amount just before the performance of the heat pipe cannot be exhibited, namely, the heat pipe reaches the heat transport limit is called the maximum heat transport amount.
Patent documents JP-A-2003-222480 and JP-A-2006-275346 describe that there are the optimum groove depths (fin heights) and groove spaces for obtaining the high maximum heat transport amount in the pipes with internal grooves.
Further, Patent document JP-A-2006-189232 describes the heat pipe which is designed to increase the maximum heat transport amount by enhancing the capillary force in the grooves between the fins by adding the second fin shape between the first fin shapes in the pipe with internal grooves.
Patent document JP-A-03-134493 discloses the structure which is designed to increase the maximum heat transport amount by separating the vapor flow and the return flow of the condensate liquid by providing an internal pipe extending to the heat radiation side from the heat receiving side in the heat pipe tube.
Patent document JP-A-61-125590 describes the structure in which by attaching a ring-shaped flat fin to the inside of the pipe with inner surface grooves for reduction in thermal resistance, the surface areas of the evaporation surface and the condensation surface are increased, and by using the inner surface grooves of the pipe for transport of the working fluid, thermal resistance is reduced while the maximum heat transport amount is kept.
Patent document JP-A-2000-35295 discloses the structure in which a region Without a groove is formed in a part of the internal groove structure in the pipe with inner surface grooves, and by flowing a condensate liquid to this region, the draining performance of the pipe is enhanced, the grooves which can be also expressed as fins are prevented from being covered with an excessive amount of the condensate liquid, and thermal resistance is reduced.